This invention relates to protective films for decorative, primarily outdoor structures, such as building siding, signs, and vehicle body panels. More specifically, it relates to a multilayer film including a weather-resistant protective layer of a fluoropolymer/acrylic polymer alloy bonded to an adjacent cushioning layer of an impact-resistant, low modulus, thermoplastic polymer.
In recent years the commercial significance of decorative marking of rigid and flexible, interior and exterior walls and panels has continued to develop. The applications for decoratively marked surfaces are pervasive. They may be found for example on outside building walls of aluminum or polyvinyl chloride (PVC) siding, fence elements, billboards and road signs, exterior truck, bus and airplane panels, and interior bulkheads of passenger cabins of boats, airplanes and railroad cars.
There has been a continuing need to protect these decoratively marked surfaces against weathering, chemical corrosion, staining and other degradation processes. A technology that has developed to serve this need involves covering a decoratively marked surface with a protective film. It has been found that films containing fluoropolymers, especially polyvinylidene fluoride (PVDF), are very weather, corrosion and stain resistant. Hence, fluoropolymers are widely used in corrosion resistant pipes, plates and sheets, and paints for protective coating or laminating of interior stain resistant articles, exterior weathering or chemical corrosion-susceptible articles, such as vinyl siding, window frames, signs, awnings, and so forth.
Unfortunately, many fluoropolymers including PVDF are also incompatible, and thus, nonadhesive to many substrates for which surface protection is often desired. One method of improving adhesion of a fluoropolymer to certain suitable substrates, such as PVC or polycarbonate, involves providing an intermediate adhesive layer comprising an acrylic resin. Because vinylidene fluoride and acrylic resin are miscible over a very wide concentration range in the amorphous state, adhesion is improved somewhat. Host ever, the fluoropolymer and adhesive layers are preferably applied simultaneously in an extrusion or lamination process. This process does not provide sufficient surface interaction between fluoropolymer and adhesive layers to overcome the inertness to the fluoropolymer so as to achieve satisfactory adhesion.
Another approach has been to mix a fluoropolymer with acrylic resin in melt or solution to make an alloy that may be coated, laminated, molded, or extrusion cast onto substrates thereby forming a monolayer protective film. Adhesion can be improved to acceptable levels when the concentration of acrylic resin in the alloy is high enough. Usually at least about 50 wt. % is used. However, such high fractions of acrylic resin increase the brittleness of the film unacceptably and cause deterioriation of resistance to ultraviolet radiation, weatherability, chemicals and stains.
A variety of technological improvements directed toward utilizing multiple layers of different compositions and blends have been proposed.
U.S. Pat. No. 4,317,860 discloses a laminate comprising a layer of PVDF and a thermoplastic resin layer joined together over their entire surface by means of an intermediate layer of a polyalkyl methacrylate which is itself intimately united to the surfaces of the two polymer layers.
U.S. Pat. No. 4,364,886 discloses a method of forming a molded laminate by either compression or injection molding a polymer which is incompatible with PVDF onto the surface of a preformed laminate of PVDF and a polyalkyl methacrylate obtained by coextrusion of the PVDF and polyalkyl methacrylate. The PVDF layer can include copolymers of PVDF with other polymers or mixtures of PVDF with other polymers.
U.S. Pat. No. 4,677,017 discloses a multilayered coextruded film comprising a thermoplastic fluoropolymer layer, an adjacent thermoplastic polymer layer and an adhesive layer of a modified polyolefin, preferably ethylene vinyl acetate copolymer. therebetween.
U.S. Pat. No. 5,180,634 discloses coextruded multilayer sheet comprising a first outer layer consisting of a blend of PVDF, homopolymer or copolymer of elastomer-grafted, alkylmethacrylate, a layer of a homopolymer or copolymer of an elastomer-grafted alkylmethacrylate, and an optional intermediate layer of a homopolymer or copolymer of an alkylmethacrylate.
U.S. Pat. No. 5,256,472 discloses a fluorine resin type weather resistant film of multi-layer structure comprising a front surface layer of a major fraction vinylidene fluoride resin and a minor fraction of methacrylate resin, and a rear surface layer of a major fraction of methacrylate resin and a minor fraction of vinylidene fluoride resin and an ultraviolet light absorber.
U.S. Pat. No. 5,506,031 discloses a process that involves transferring a decoratine coating on a matte release layer onto an extruded plastic sheet. The release layer contains a low gloss agent and the decorative coating is transferred while pressure is applied by an embossing roll that forms deep three dimensional impressions in the outer surface of the decorative coating to provide a low gloss decorative coating that resembles natural wood grain.
WO 94/12583 discloses a heat transferable fluorinated resin multilayer film having a surface layer comprising a resin composition containing at least 60 wt % vinylidene fluoride resin and an adhesive layer of mainly a transparent acrylic resin having a glass transition temperature of 35xc2x0 C.-90xc2x0 C. The film can be laminated at a low heat transfer temperature of at most 110xc2x0 C.
While these and other techniques have achieved some success in balancing weather, corrosion and stain resistance properties with adhesion of the protective coating to a substrate other problems remain. For example, traditional multilayer coatings are generally unable to adequately protect against scratching, chipping, cracking, peeling and similar deterioration resulting from the cumulative effect of impacts by foreign materials. For example, exterior vehicle body panels are constantly subject to being struck at high speed by dust, dirt and grit particles causing damage to the protective coating. Simlilarly, contact by wind-borne dirt, hail and contact with nearby objects is known to damage stationary surface coatings. Additionally, traditional protective coatings are typically rigid and brittle. Although very adhesive, they are susceptible to delamination from flexible or deflecting substrates such as thin sections of expansive building siding and awnings.
The protective coating for decoratively marked surfaces should excel in impact resistance, and optionally, in other performance criteria as well as being weather resistant, stainproof and adhesive. For example, in many applications they should be clear so that the underlying decoration shows through without distortion or haze. Yet further, it is often desired that the protective coating have a prescribed level of gloss or lack thereof. Hence, there still remains a need for a weatherproof, stainproof, adhesive, preferably clear protective coating adapted to providing a preferably low, preselected glossiness that also is highly impact resistant and is durable on flexible and deflecting substrates.
Accordingly, there is now provided by this invention a multilayer film comprising a protective layer of a blend comprising a fluorine substituted olefin polymer and an acrylic polymer, the protective layer being firmly bonded to a cushioning layer comprising an impact resistant polymer having an elastic modulus of less than 207 MPa and substantially free of any fluoropolymer.
There is also provided a multilayer film as just described further comprising a thermally adhesive layer bonded to the cushioning layer opposite the protective layer. which thermally adhesive layer comprises a blend comprising a fluorine substituted olefin polymer and an acrylic polymer. Each of the flourine substituted olefin polymer, acrylic polymer and impact resistant polymer components can independently comprise homopolymer, copolymer and blends thereof, respectively. The thermally adhesive layer provides strong bonding of the multilayer film to many substrate materials without the need for additional adhesive agents or primers.
Still further there is provided weather and stain resistant composite structure comprising
a substrate having a decorative surface, and
a multilayer film covering the substrate and comprising a protective layer of a blend comprising a fluorine substituted olefin polymer and an acrylic polymer, the protective layer being firmly bonded to a cushioning layer comprising an impact resistant polymer having an elastic modulus of less than 207 MPa and substantially free of any fluoropolymer,
in which the decorative surface is thermally bonded to the cushioning layer.
The novel multilayer films and composite are useful for vibrantly and durably decorated vehicle body panels, building exteriors, flexible awnings, signs, bulkheads in passenger quarters of automobiles, trucks, trains, and airplanes, and the like.